Process for extracting carboxylic acids produced by anaerobic fermentation from fermentable biomass

Abstract

The process involves extracting carboxylic acids having from one to nine carbons, the carboxylic acids produced by microorganisms in a fermentation reactor by anaerobic fermentation from fermentable biomass. The extraction is a liquid-liquid type, and includesa) choosing an endogenous extraction solvent among at least one of the carboxylic acids, such that the number of carbons of the solvent is greater than or equal to the number of carbons of the carboxylic acid to be extracted,b) bringing the extraction solvent chosen into contact with the fermentation medium, without interrupting the fermentation, outside the fermentation reactor,c) separating (6) the fermentative metabolites from the extraction solvent by at least one distillation, andd) collecting and storing or using the fermentative metabolites obtained in step c).The invention also relates to a facility for carrying out the process.

The invention claimed is: 
     
       1. A process for directly extracting carboxylic acids having from one to nine carbons, produced by a mixture of eukaryotic and prokaryotic microorganisms in a fermentation reactor by anaerobic fermentation of an untreated fermentable biomass, said extraction being of a liquid-liquid type, without significantly lowering pH of a fermentation medium, said process comprising:
 a) initiating the extraction process when production of the carboxylic acids having from one to nine carbons reaches a predefined amount in the fermentation reactor, the predefined amount corresponding to a slowing of growth of the eukaryotic and prokaryotic microorganisms in the fermentation reactor, the slowing of growth lying in a region of microorganism inhibition threshold linked to an acidification of the fermentation medium, 
 b) choosing an endogenous extraction solvent among carboxylic acids having at least four carbons produced during the anaerobic fermentation of the untreated fermentable biomass, such that the number of carbons of the endogenous extraction solvent is greater than or equal to the number of carbons of the carboxylic acids to be extracted, wherein the endogenous extraction solvent has a density below that of water and a boiling point above 70° C. under normal pressure conditions, 
 c) bringing the endogenous extraction solvent into contact with a portion of fermentation medium from the fermentation reactor containing at least the carboxylic acids having from one to nine carbons outside the fermentation reactor, without halting the fermentation inside the fermentation reactor, 
 d) directly extracting the carboxylic acids having from one to nine carbons from the fermentation medium through contact with the endogenous extraction solvent under conditions which are non-lethal for the eukaryotic and prokaryotic microorganisms, 
 e) separating the carboxylic acids having from one to nine carbons from the endogenous extraction solvent, obtained after liquid-liquid type extraction at step d), through at least one distillation, 
 f) collecting and storing or using the carboxylic acids having from one to nine carbons obtained in step e), 
 wherein directly extracting the carboxylic acids in step d) reduces the acidification of the fermentation medium during the anaerobic fermentation, which maintains activity of the eukaryotic and prokaryotic microorganisms in the fermentation reactor for continuing the anaerobic fermentation. 
 
     
     
       2. The process as claimed in  claim 1 , wherein, after step e) and before step f), carboxylic acids are separated by distillation during an additional step g), from water of an organic phase obtained in step e). 
     
     
       3. The process as claimed in  claim 1 , wherein the extraction solvent is a carboxylic acid having from four to nine carbons. 
     
     
       4. The process as claimed in  claim 3 , wherein the extraction solvent is a carboxylic acid having seven or eight carbons. 
     
     
       5. The process as claimed in  claim 1 , wherein the extraction solvent is chosen from heptanoic acid, octanoic acid or nonanoic acid. 
     
     
       6. The process as claimed in  claim 1 , wherein a decanting step h), between steps e) and f), allows a first separation between organic and aqueous phases. 
     
     
       7. The process as claimed in  claim 1 , wherein, during the bringing of the fermentation medium into contact with the extraction solvent outside the reactor, the fermentation medium is taken continuously. 
     
     
       8. The process as claimed in  claim 1 , wherein, during the bringing of the fermentation medium into contact with the extraction solvent outside the reactor, the fermentation medium is taken sequentially. 
     
     
       9. The process as claimed in  claim 1 , wherein, after step e), at least one part of a residual liquid phase resulting from the extraction, containing active microorganisms, is reintroduced into the fermentation reactor and incorporated into the fermentation medium without significantly lowering the pH of the fermentation medium.